sign in sign up
<<
Home , Barn (unit), True muonium

KEK-PH Lectures and Workshops

Hadron Physics

Zhen Liu University of Maryland 08/05/2020 Part I: Basics Part II: Advanced Topics Focus Collider Physics is a vast topic, one of the most systematically explored areas in physics, concerning many observational aspects in the microscopic world • Focus on important collider concepts and representative examples • Details can be studied later when encounter References: Focus on basic pictures Barger & Philips, Collider Physics Pros: help build intuition Tao Han, TASI lecture, hep-ph/0508097 Tilman Plehn, TASI lecture, 0910.4182 Pros: easy to understand Maxim Perelstein, TASI lecture, 1002.0274 Cons: devils in the details Particle Data Group (PDG) and lots of good lectures (with details) from CTEQ summer schools

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 2 Part I: Basics The Lyndon R Evans DOI:10.1098/rsta.2011.0453 Path to discovery 1995 1969

1974 1969 1979 1969 1800-1900 1977

2012

2000 1975 1983 1983

1937 1962 Electric field to accelerate 1897 1956 charged Synchrotron radiation 𝐸𝐸 4 𝑚𝑚

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 4 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 5 Why study (hadron) (now)? • Leading tool in probing microscopic structure of nature • history of discovery • Currently running LHC • Great path forward

• Precision QFT including strong dynamics and weakly coupled theories • Application to other physics probes • Set-up the basic knowledge to build other subfield of elementary

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 6 Basics: Experiment & Theory

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 7 Basics: How to make measurements?

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 8 Part I: Basics Basic Parameters Basics: Smashing & Quick Estimates Size ( ) Proton-Proton ( ) Particle Physicists𝑂𝑂 𝑓𝑓𝑓𝑓 use the unit “Barn”2 1 = 100𝑂𝑂 𝑓𝑓𝑚𝑚 The American idiom "couldn't hit the broad side of a barn" refers to someone whose aim is very bad. Enrico Fermi said the neutrons2 hits nuclear reactor nucleus as easy as hitting𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 the broad side of a barn.𝑓𝑓𝑚𝑚 Proton-Proton cross section is then 10 , actually ~20 mb for hard and 100 mb for total scattering. 𝑂𝑂 𝑚𝑚𝑚𝑚

In ( ~)200 1 −1 Zhen Liu Hadron Collider Physics (lecture) Λ 𝑄𝑄𝑄𝑄𝑄𝑄 KEK 2020 𝑀𝑀𝑀𝑀𝑀𝑀 ≃ 𝑓𝑓𝑚𝑚 10 Basics: Smashing Protons & Quick Estimates Particle Physicists use the unit “Barn” Beam of colliding 1 = 100 = 10 particles are the Proton-Proton cross section2 is ~100−28 mb2 for microscope for us. total scattering.𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑓𝑓𝑚𝑚 𝑚𝑚 LHC is 3 Beam power is called (# / /sec) ILC 250 GeV− 12 Instantaneous Luminosity, typical value2 is 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑐𝑐𝑚𝑚 FCC-ee/CEPC𝑎𝑎𝑏𝑏 5 −1 10 = 10 FCC-hh 30 𝑎𝑎𝑏𝑏 −1 A typical year34 is− 210 sec−1 , for 10 years−1 , −1 𝑐𝑐𝑚𝑚 𝑠𝑠𝑒𝑒𝑒𝑒 𝑛𝑛𝑏𝑏 𝑠𝑠𝑒𝑒𝑒𝑒 −1 𝑎𝑎𝑏𝑏 accumulating Integrated7 Luminosity, 𝑎𝑎𝑏𝑏 = 10 = 1 9 −1 −1 𝐿𝐿 𝑛𝑛𝑏𝑏 𝑎𝑎𝑏𝑏 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 11 Basics: typical cross sections Amongst the collisions, most are not of too much interests to us (either soft scattering, corresponding to known low energy physics, or too massy to interpret), only a small fraction of the collisions are our primary targets. At 14 TeV LHC: How did we calculate the rate Inclusive: 100 and develop a strategy to Dijets (pT> 50 GeV):discover 20 Higgs at the LHC? W: 200 𝑚𝑚𝑚𝑚 Z: 50 𝜇𝜇𝜇𝜇 Top 𝑛𝑛𝑛𝑛 pair: 800 WW: 100𝑛𝑛𝑛𝑛 H: 50 (× =𝑝𝑝150𝑝𝑝 ) : 10 𝑝𝑝𝑝𝑝 −1 𝑝𝑝𝑝𝑝 3𝑎𝑎𝑏𝑏 𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀 𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻 Zhen Liu𝛾𝛾𝛾𝛾 𝑝𝑝Hadron𝑝𝑝 Collider Physics (lecture) KEK 2020 12 Part I: Basics Basic Parameters Basic Cross Sections & Representation At hadron colliders, we are smashing protons. Cross Sections Protons are composite. We are colliding the constituents. 𝝈𝝈 ( ) = × × 𝟐𝟐 𝝈𝝈𝒊𝒊→𝒇𝒇 𝑺𝑺 𝒇𝒇𝒇𝒇𝒇𝒇𝒙𝒙𝒊𝒊 𝑴𝑴𝒊𝒊→𝒇𝒇 𝑷𝑷𝑺𝑺𝒇𝒇 Center of 1 Mass 4 Energy × 𝑖𝑖 𝑓𝑓 𝛿𝛿 Σ𝑝𝑝 − Σ𝑝𝑝 4 .. 2 0 𝑑𝑑 𝑝𝑝𝑗𝑗 � 𝛿𝛿 𝑝𝑝𝑗𝑗 𝜃𝜃 𝑝𝑝𝑗𝑗 3 2𝑆𝑆 𝑗𝑗=1 𝑓𝑓 2𝜋𝜋 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 14 Partonic Cross Sections (Hard Scattering)

“Parton”—proton constituents𝝈𝝈� ( ) = × × 𝟐𝟐 𝝈𝝈�𝒊𝒊→𝒇𝒇 𝒔𝒔� 𝒇𝒇𝒇𝒇𝒇𝒇𝒙𝒙𝒊𝒊 𝑴𝑴𝒊𝒊→𝒇𝒇 𝑷𝑷𝑺𝑺𝒇𝒇 Partonic 1 4 Center of × 𝑖𝑖 𝑓𝑓 𝛿𝛿 Σ𝑝𝑝 − Σ𝑝𝑝 4 Mass .. 2 0 𝑑𝑑 𝑝𝑝𝑗𝑗 2 � 𝛿𝛿 𝑝𝑝𝑗𝑗 𝜃𝜃 𝑝𝑝𝑗𝑗 3 Energy 𝑗𝑗=1 𝑓𝑓 2𝜋𝜋 < 𝑠𝑠̂ Zhen Liu 𝒔𝒔� Hadron𝑺𝑺 Collider Physics (lecture) KEK 2020 15 Hadron Collider Representation lab frame center of mass frame but can be translated via Lorentz Boost in the Z-direction = ( , 0≠,0, ), = ( , 0,0, ) Collider (Beam) center of mass energy = , e.g., LHC is 14 TeV with 7 TeV on each beam, ILC 250 is 250 GeV S with 125 GeV on each1 beam. 2 2 Hadron colliders can only use𝑃𝑃 part of 𝐸𝐸the𝑆𝑆 total2𝐸𝐸 energy𝐸𝐸 𝑃𝑃 as it effectively𝐸𝐸 colliding−𝐸𝐸 partons = ( , 0,0, ), = ( , 0,0, ) Viewing parton 1 and 2 as a system, its Invariant mass (c.o.m.1energy): 1 1 2 2 2 𝑝𝑝 =𝑥𝑥 𝐸𝐸 + 𝑥𝑥 𝐸𝐸= 𝑝𝑝 𝑥𝑥 𝐸𝐸= −𝑥𝑥 𝐸𝐸 Velocity ( ) & Rapidity ( ) in lab frame: 2 1 2 1 2 1 2 𝛽𝛽 𝑌𝑌=𝑠𝑠̂ ( 𝑝𝑝 )𝑝𝑝/( +𝑥𝑥 𝑥𝑥), Y2𝐸𝐸= log𝑥𝑥(𝑥𝑥 /𝑆𝑆 ) 1 𝛽𝛽 𝑥𝑥1 − 𝑥𝑥2 𝑥𝑥1 𝑥𝑥2 2 𝑥𝑥1 𝑥𝑥2 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 16 Rapidity Rapidity: 1 + ln 2 𝐸𝐸 𝑝𝑝𝑧𝑧 General 4-momenta: 𝑦𝑦 ≡ 𝑧𝑧 = cosh , sin 𝐸𝐸, − 𝑝𝑝cos , sinh with +𝑝𝑝 , 𝐸𝐸𝑇𝑇 𝑦𝑦 +𝑝𝑝𝑇𝑇 𝜙𝜙 𝑝𝑝𝑇𝑇 𝜙𝜙 𝐸𝐸𝑇𝑇 𝑦𝑦 2 2 2 2 Rapidity𝑝𝑝𝑇𝑇 ≡ is additive𝑝𝑝𝑥𝑥 𝑝𝑝𝑦𝑦 for𝐸𝐸𝑇𝑇 boost≡ 𝑝𝑝 𝑇𝑇along𝑚𝑚 z-direction (reference rapidity of ) = 0 ′ 𝑦𝑦Very useful Rapidity difference invariant under boost 0in z-direction 𝑦𝑦 =𝑦𝑦 − 𝑦𝑦 properties for hadron colliders, Hence allow trivial differential′ translation′ (Jacobian of 1) 𝑦𝑦𝑎𝑎 − 𝑦𝑦𝑏𝑏 𝑦𝑦𝑎𝑎 − 𝑦𝑦𝑏𝑏 which needs boost = in the z-direction 𝑑𝑑 𝑑𝑑 ′ Zhen Liu Hadron Collider Physics𝑑𝑑 𝑑𝑑(lecture)𝑑𝑑𝑦𝑦 KEK 2020 17 Rapidity & Pseudo Rapidity Rapidity: Pseudo-Rapidity: 1 + 1 + ln ln 2 2 𝐸𝐸 𝑝𝑝𝑧𝑧 𝑝𝑝⃗ 𝑝𝑝𝑧𝑧 Rapidity is𝑦𝑦 additive≡ for boost𝑧𝑧 along z- For massless𝜂𝜂 particles≡ 𝑧𝑧 direction (reference𝐸𝐸 rapidity− 𝑝𝑝 of ) =𝑝𝑝⃗ − 𝑝𝑝 = 0 inherit all the properties. ′ 𝑦𝑦 𝜂𝜂 𝑦𝑦 Rapidity difference invariant0 under In the limit of boost in z-direction𝑦𝑦 𝑦𝑦 − 𝑦𝑦 = 𝐸𝐸 ≫ 𝑚𝑚 ′ ′ all the properties approximately hold Hence allow𝑎𝑎 trivial𝑏𝑏 differential𝑎𝑎 𝑏𝑏 𝜂𝜂 ≈ 𝑦𝑦 translation𝑦𝑦 (Jacobian− 𝑦𝑦 𝑦𝑦 of− 1)𝑦𝑦 = No above properties for massive particles 𝑑𝑑 𝑑𝑑 ′ 𝑑𝑑𝑑𝑑 𝑑𝑑𝑦𝑦 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 18 Pseudo Rapidity representing Geometry Pseudo-Rapidity: 1 + 1 1 + cos ln = ln = ln cot 2 2 1 cos 2 𝑝𝑝⃗ 𝑝𝑝𝑧𝑧 𝜃𝜃 𝜃𝜃 𝜂𝜂 ≡ Recall that two-body phase 𝑝𝑝⃗ − 𝑝𝑝𝑧𝑧 − 𝜃𝜃 space = cos Compared 1to cos , is 𝑃𝑃𝑆𝑆2 8𝜋𝜋 𝑑𝑑 𝜃𝜃 preferred phase space measure, e.g., a spinless particle𝜃𝜃 decay𝜃𝜃 is “flat” in cos not

Approximately linear (in both cos and ) in𝜃𝜃 the 𝜃𝜃 central region (|cos | < 1) “zoom in” for forward region (|cos𝜃𝜃 |~1)𝜃𝜃 𝜃𝜃 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 𝜃𝜃 19 Pseudo Rapidity representing Geometry Pseudo-Rapidity: 1 + 1 1 + cos ln = ln = ln cot 2 2 1 cos 2 𝑝𝑝⃗ 𝑝𝑝𝑧𝑧 𝜃𝜃 𝜃𝜃 𝜂𝜂 ≡ 𝑝𝑝⃗ − 𝑝𝑝𝑧𝑧 − Experimentally,𝜃𝜃 the hadron collider geometry are expressed in pseudo rapidity

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 20 Pseudo Rapidity representing Geometry Pseudo-Rapidity: 1 + 1 1 + cos ln = ln = ln cot 2 2 1 cos 2 𝑝𝑝⃗ 𝑝𝑝𝑧𝑧 𝜃𝜃 𝜃𝜃 𝜂𝜂 ≡ 𝑝𝑝⃗ − 𝑝𝑝𝑧𝑧 − Experimentally,𝜃𝜃 the hadron collider geometry are expressed in pseudo rapidity

Typical high mass/energy events (central: Barrel & EndCap): | | < 3 Forward (lots of QCD background) 𝜂𝜂 > 3

𝜂𝜂 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 21 Part I: Basics Basic Parameters Basic Cross Sections & Representation Parton Distribution Functions Factorization Short distance physics (large momentum transfer) should not depend on long distances physics.

= ,

𝜎𝜎𝑝𝑝𝑝𝑝→𝑓𝑓 𝑆𝑆 ∫ 𝑑𝑑𝑥𝑥1𝑑𝑑𝑥𝑥2Σ𝑎𝑎 𝑏𝑏𝑓𝑓𝑎𝑎 𝑥𝑥1 𝑓𝑓𝑏𝑏 𝑥𝑥2 𝜎𝜎�𝑎𝑎𝑎𝑎→𝑓𝑓 𝑠𝑠̂ Used as working assumption = QCD factorization proven for certain processes QED factorization proven 𝑠𝑠̂ 𝑥𝑥1𝑥𝑥2𝑆𝑆

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 23 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 24 Parton Distribution Functions (PDFs) Partons are weakly bound (when probed) constituents of . Feynman; Bjorken, Paschos-1969

Collinear PDFs ( , ) are the simplest functions describing the nonperturbative hadron structure. 𝑓𝑓𝑎𝑎 𝑥𝑥 𝑄𝑄 (In the simplest interpretation) ( , ) is the probability to find a parton a carrying momentum of the initial 𝑎𝑎 hadron with momentum , with𝑓𝑓 a𝑥𝑥 probing𝑄𝑄 𝜇𝜇 scale of . 𝜇𝜇 𝑥𝑥𝑝𝑝 𝑝𝑝 𝑄𝑄 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 25 Parton Distribution Functions (PDFs) PDFs ( , ) are universal, independent of the hard- scattering process. 𝑓𝑓𝑎𝑎 𝑥𝑥 𝑄𝑄 The structure of the hadron drastically as a function of the probing scale Q, obeying Dokshitzer-Gribov-Lipatov- Altarelli-Parisi (DGLAP) equations ( , ) = , ( , ) 1 / 𝑖𝑖 , , , , ,… 𝑑𝑑𝑓𝑓 𝑥𝑥 𝜇𝜇 𝑑𝑑𝑑𝑑 𝑖𝑖 𝑗𝑗 𝑥𝑥 𝑆𝑆 𝑗𝑗 𝜇𝜇 � �𝑥𝑥 𝑃𝑃 𝛼𝛼 𝜇𝜇 𝑓𝑓 𝑦𝑦 𝜇𝜇 𝑑𝑑𝑑𝑑 � � 𝑦𝑦 𝑦𝑦 / are the probabilities𝑗𝑗=𝑔𝑔 𝑢𝑢 𝑢𝑢 𝑑𝑑 𝑑𝑑 for colinear splitting.

𝑖𝑖 𝑗𝑗 𝑃𝑃Zhen Liu Hadron Collider Physics (lecture)𝑗𝑗 → 𝑖𝑖 KEK𝑖𝑖 2020 26 Hard: large momentum transfer Soft: small momentum transfer Zhen Liu Hadron Collider Physics (lecture) KEK 2020 27 Reasonable (boundary conditions) for PDFs Momentum sum-rule (conservation) , = 1 1 , , , , ,… 𝑎𝑎 � �0 𝑥𝑥𝑓𝑓 𝑥𝑥 𝑄𝑄 𝑑𝑑𝑑𝑑 Valence sum rule,𝑎𝑎 =e.g.,𝑔𝑔 𝑢𝑢 𝑢𝑢� for𝑑𝑑 𝑑𝑑� protons (uud) [ , , ] = 2 1 𝑢𝑢 𝑢𝑢� � [𝑓𝑓 𝑥𝑥, 𝑄𝑄 − 𝑓𝑓 𝑥𝑥,𝑄𝑄 ]𝑑𝑑𝑑𝑑 = 1 01 𝑑𝑑 � � [𝑓𝑓 𝑥𝑥,𝑄𝑄 − 𝑓𝑓𝑑𝑑 𝑥𝑥, 𝑄𝑄 ] 𝑑𝑑𝑑𝑑= 0 Sea quark 0 1 � 𝑓𝑓𝑠𝑠 𝑥𝑥 𝑄𝑄 − 𝑓𝑓𝑠𝑠̅ 𝑥𝑥 𝑄𝑄 𝑑𝑑𝑑𝑑 Zhen Liu Hadron Collider0 Physics (lecture) KEK 2020 28 Recall that Up and Down are valence , their PDF have a peak at x~1/3, valence quark effect at low 2 PDF rise rapidly𝑄𝑄 at low x due to perturbative evolution (splitting)

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 29 As Q increases, high x partons lose momentum through QCD radiation

Up Quark PDF evolution (splitting)

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 30 As Q increases, high x partons lose momentum through QCD radiation (splitting), PDF Gluon PDF evolution dominants and sea quark Up anti-quark PDF evolution PDF follows

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 31 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 32 PDF (as a function of )

= 𝑠𝑠̂ , = 𝜎𝜎𝑝𝑝𝑝𝑝→𝑓𝑓 𝑆𝑆 1 2 𝑎𝑎, 𝑏𝑏 𝑎𝑎 1 𝑏𝑏 2 (𝑎𝑎𝑎𝑎)→𝑓𝑓 ∫ 𝑑𝑑𝑥𝑥 𝑑𝑑𝑥𝑥1 Σ 𝑓𝑓 𝑥𝑥 𝑓𝑓 𝑥𝑥 𝜎𝜎� 𝑠𝑠̂ ∫ 𝑑𝑑Useful𝑠𝑠̂𝑑𝑑𝑑𝑑 𝑠𝑠tô Σ 𝑎𝑎quickly𝑏𝑏𝑥𝑥1𝑓𝑓𝑎𝑎 estimate𝑥𝑥1 𝑥𝑥2𝑓𝑓𝑏𝑏 high𝑥𝑥2 energy𝜎𝜎�𝑎𝑎𝑎𝑎→𝑓𝑓 𝑠𝑠̂ physics processes

PDF drops as a high power (5-6 power) as a function of the enter of mass energy

𝑠𝑠̂

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 33 “Inverse Process” of fragmentation and hadronization

Fig. Credit: Zhen Liu Hadron Collider Physics (lecture) KEK 2020 Eric M. Metodiev 34 Part I: Basics Basic Parameters Basic Cross Sections & Representation Parton Distribution Functions Detection How do we see SM particles

New physics canDirectly be of “seen” any of these forms and “Seen” via reconstruction even more exoticof secondary vertex

“Reconstructable”

Missing (transverse) energy 𝜈𝜈

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 36 Directly Seen via Tracker ECal HCal Chamber

𝜇𝜇

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 37 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 38 Jet reconstruction algorithms Pile-up removal …

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 39 Part I: Basics Basic Parameters Basic Cross Sections & Representation Parton Distribution Functions Detection Simulation Phenomenological Studies Recommend, use Madgraph and the tool-chains there*

Physics First (before trusting simulations due to complex nature of QFT).

*HELAS written at KEK

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 41 How did we discover the Higgs?

Part I: Basics Basic Parameters Basic Cross Sections & Representation Parton Distribution Functions Detection Simulation Higgs Couplings • Gauge coupling • Yukawa coupling—new forces (9+ Yukawas) • Self coupling—new force • Loop-induced (anomalous) couplings , , , …

𝐻𝐻𝐻𝐻𝐻𝐻 𝐻𝐻𝐻𝐻𝐻𝐻 𝐻𝐻𝐻𝐻𝐻𝐻

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 46 Higgs Width and Branching Fractions

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 47 Higgs Physics =𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁12.937 𝑝𝑝𝑝𝑝 ×𝜎𝜎 1 + 1𝑔𝑔𝑔𝑔.28→+𝐻𝐻0.77

𝑝𝑝𝑝𝑝

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 48 A snapshot before discovery

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 49 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 50 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 51 KEK-PH Lectures and Workshops

Hadron Collider Physics

Zhen Liu University of Maryland 08/05/2020 Part I: Basics Part II: AdvancedSelected Topics Topics Part II: Selected Topics Current Status & Bright Future Zhen Liu Hadron Collider Physics (lecture) KEK 2020 54 • FCC-pp at ~40 TeV Other ideas • collider Future Collider Options • Plasma Wakefield Acceleration-based e+e- linear collider LHC End of- HL

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 55 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 56 Snowmass Planning Timeline

● Snowmass scientific study will identify and document a scientific vision for the future of particle physics in the U.S. and its international partners. ● P5 will take the scientific input from Snowmass and develop a strategic plan for U.S. particle physics that can be executed over a 10-year timescale, in the context of a 20-year global vision for the field.

● Letters of Interest (submission : April 1, 2020 – August 31, 2020) – Maximum of 2 pages of text, plus relevant bibliography – Informal documents intended to be useful in the first stages of the Snowmass study. – Help conveners to prepare the Snowmass Community Planning Meeting – Include opinions, interests and proposals that could further be studied. – Authors of the letters are welcome to make a full write-up for their work as a contributed paper (not required)

● Contributed (“white”) Papers (submission : April 1, 2020 – July 31, 2021) – Specific scientific areas, technical articles presenting new results on relevant physics topics, and reasoned expressions of physics priorities, including those related to community involvement. – Part of Snowmass proceedings. Remain part of the permanent record of Snowmass 2021 – LoIs are not required in order to submit contributed papers – These papers and discussions throughout the Snowmass process will help shape the long-term strategy of particle physics in the U.S.

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 57 Snowmass 2021 Timeline Planning Meeting Oct 5-9, 2020 Today (/Remote) 11/19 12/19 1/20 2/20 3/20 4/20 5/20 6/20 7/20 8/20 9/20 10/20

Preparation Letters of Interest

Contributed Papers

Summer Study Snowmass July 11-20, 2021 (UW Seattle) Report 11/20 12/20 1/21 2/21 3/21 4/21 5/21 6/21 7/21 8/21 9/21 10/21

Contributed Papers

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 58 Physics-wise: where are we now? A paradigm shift driven by LHC Models solving multiple puzzle of Nature at once  Models solving >=0 puzzles *but* raising new signatures that can be probed by experiments

LHC experimental colleagues have been working hard and creatively on the more established model paradigms, steady & impressive progress all the time; Our job becomes to Identify: • new opportunities that are missed or overlooked; • new important questions that could be answered; • new interesting questions about particle physics;

59 BSM Opportunities

Around the Higgs Theoretically GoTestable Exotic Experimentally Physics plausible OpportunitiesHave Fun accessible

Join Snowmass, help shaping the future of the field https://snowmass21.org/energy/start

60 Part II: Selected Topics Current Status & Bright Future Higgs Precision Zhen Liu Hadron Collider Physics (lecture) KEK 2020 62 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 63 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 64 Part II: Selected Topics Current Status & Bright Future Higgs Precision BSM Broad Brush Resonances v.s. Precision New Resonances Rich Pheno

1910.11775 1311.2099

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 66 New Resonances

• Leptophobic scenarios (Z’→tt, W’→tb, …) • Diboson resonance searches • Searches with 3rd generation particles (Z’ → tau) • ….

Important to address experimental challenges e.g. high pT reconstruction, fully exploit boosted topologies, develop state-of-the-art W/top/Higgs taggers.

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 67 New Resonances ()

• Excited quarks/ • Top partners (e.g. Vector-like quarks) • ... 1812.0783 11812.07831

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 68 Dark Sector, light resonance & LLPs

Categorization of messenger Coupling structure very rich & Very active field: fields: New trigger & analysis ideas • Scalar messenger (New) satellite exp proposals • Interfacing with other frontiers (e.g., Rare & • ( + )( ) 𝑠𝑠 Precision frontier, cosmo frontier) • Vector𝜖𝜖Λ 𝐻𝐻messenger+ 𝐻𝐻 𝑠𝑠+ • 𝜖𝜖 𝐻𝐻 𝐻𝐻 𝑠𝑠 𝑠𝑠 ′ 𝐴𝐴𝜇𝜇 • 𝜇𝜇𝜇𝜇 ′ 𝜖𝜖𝐹𝐹 𝐹𝐹𝜇𝜇𝜇𝜇 • 𝜇𝜇 messenger′ 𝑆𝑆𝑆𝑆 𝜇𝜇 • 𝜖𝜖(𝐽𝐽 𝐴𝐴) • messenger 𝑁𝑁 • 𝜖𝜖 (𝐿𝐿𝐿𝐿 𝑁𝑁 + + ) 𝑎𝑎 𝛼𝛼3 𝛼𝛼2 𝑎𝑎 𝑓𝑓𝑎𝑎 8𝜋𝜋 𝐺𝐺𝐺𝐺� 8𝜋𝜋 𝑊𝑊𝑊𝑊� ⋯ 1910.11775 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 69 An example: Heavy Axion V’(a) Mass of the axion is a robust prediction cos( + ) 𝑄𝑄𝑄𝑄𝑄𝑄 2 2 𝑎𝑎 New contributions to 𝜋𝜋the 𝜋𝜋potential and the 𝑉𝑉 𝑎𝑎 ≃ −𝑓𝑓 𝑚𝑚 𝜃𝜃 𝑎𝑎 mass in general will not be aligned𝑓𝑓 with the QCD potential = + cos( + ) 𝑛𝑛 𝑄𝑄𝑄𝑄𝑄𝑄 𝑓𝑓𝑎𝑎 𝑎𝑎 Rubakov,𝑉𝑉 97’𝑎𝑎 𝑉𝑉 𝑛𝑛−4 𝜃𝜃′ 2 Hook, 14’ 𝑎𝑎 QCD Dimopoulos, Hook, Huang, MarquesΛ-Tavares, 16’ 𝑓𝑓 V(a) Λ′ Gherghetta, Nagata, Shifman, 16’ 𝑎𝑎 Argarwal, Howe, 17’ 𝑚𝑚 ≃ 𝑎𝑎 Argarwal, Howe, 17’ 𝑓𝑓 Hook, Kumar, ZL, Sundrum, 19’ Csaki, Ruhdorfer, Shirman, 19’ Gherghetta, Khoze, Pomarol, Shirman, 20’ = 0 / Zhen Liu Hadron Collider Physics (lecture) KEK 2020 70 𝑎𝑎 𝜃𝜃̅ 𝑎𝑎 𝑓𝑓 Heavy Axion: challenge & opportunity Challenge: light, rarely produced, hadronic states;

Big open windows for well-motivated heavy

Opens a new direction of singly produced long- lived particles.

A lot more to explore.

Hook, Kumar, ZL, Sundrum, 19’ + + 8 𝛼𝛼𝑠𝑠 𝑎𝑎 𝜃𝜃 𝐺𝐺�𝐺𝐺 ⋯ 𝜋𝜋 𝑓𝑓𝑎𝑎 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 71 Model Agnostic Searches Lot of interest in using Machine Learning/AI techniques

Anomaly detection at both trigger and analysis level

Also other techniques for special, unexpected signals: Zero-bias events, data parking, early-alarming, etc. D. Shih et al, 2001.05001,2001.04990

Fig. from J. Thaler’s Pheno 2019 talk also M. Perelstein’s ML4jets 2020 talk Zhen Liu Hadron Collider Physics (lecture) KEK 2020 72 Part II: Selected Topics Current Status & Bright Future Higgs Precision BSM Broad Brush Rethink about Long-Lived Particles First pixel layer (first What is LLP? layer of detector)

Long-lived particles in the : • approximate symmetries; • kinematic suppressions; Detector tagged and energy detectable For BSM particles: • Prompt particles being actively probed; • Detector Stable particles are probed as missing energy or EM charged stable particles.

Fig. credit: L. Lee @ ATLAS Zhen Liu Hadron Collider Physics (lecture) KEK 2020 4 Why Long-Lived BSM Particles? Supersymmetry

• R-Parity-Violating, small B/L-violating couplings 100 GeV 10 ~1 m −8 2 𝑅𝑅𝑅𝑅𝑅𝑅 𝑐𝑐𝜏𝜏 𝑅𝑅𝑅𝑅𝑅𝑅 • Gauge mediation—suppressed𝑚𝑚� couplings𝜆𝜆 via SUSY breaking scale 100 GeV ~10 m 4 5 100 TeV 𝐹𝐹 𝑐𝑐𝜏𝜏GMSB 𝑚𝑚� • Mini-split spectrum—suppressed couplings through “decoupled” heavy particles

TeV ~1 mm 5 PeV 4 𝑚𝑚𝑞𝑞� 𝑐𝑐𝜏𝜏milli−split • Pure Wino/–nearly degenerated,𝑚𝑚𝑔𝑔� disappearing track Zhen Liu Hadron Collider Physics (lecture) KEK 2020 75 Why Long-Lived BSM Particles? Hidden Valley Hidden sector feeble couplings to SM via various portals, suppressed by the Higgs Dark smallness of the couplings portal /Z

Zurek, Strassler

Neutrino Axion(-like Portal particle) Portal

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 76 LLP: A rich program

LHC detectors designed for prompt signals. For LLPs:

trigger reconstruction standard model background non-standard background

Huge uncharted well-motivated territories to explore!

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 Fig. credit: Heather Russel @ ATLAS 13 Forward Spectrometer Expanding the LHC program MATHUSLA Codex-B AL3X Central/Hard LLPs ANUBIS FASER SHiP Forward/lighter LLPs Search for LLPs NA62 Beamdump experiments SeaQuest … monopole MoEDAL millicharged particles MilliQan

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 78 What are these proposals?

MATHUSLA

Codex-B LHC Beam AL3XAL3X ATLAS & CMS

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 79 What are these proposals?

MATHUSLA

Codex-B

AL3X ATLAS & CMS

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 80 Universal features of LLPs: a typical reach plot

Log scale in sensitivity in model parameters or observable rate (e.g., Br H->XX)

Better sensitivity Log scale in proper lifetime Zhen Liu Hadron Collider Physics (lecture) KEK 2020 81 Universal features of LLPs: understanding shapes

Log scale in sensitivity in model parameters or observable rate (e.g., Br H->XX)

Geometrical acceptance Pin

=

𝑑𝑑 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 Better sensitivity Log scale in proper lifetime Zhen Liu Hadron Collider Physics (lecture) KEK 2020 82 Universal features of LLPs: understanding shapes

Log scale in sensitivity in model parameters or observable rate (e.g., Br H->XX)

Geometrical acceptance Pin

=

Double𝑑𝑑 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 LLPs: Better sensitivity 2 𝑃𝑃in Log scale in proper lifetime Zhen Liu Hadron Collider Physics (lecture) KEK 2020 83 Countering one’s intuition

Log scale in sensitivity in model parameters or observable rate (e.g., Br H->XX)

• For short lifetime: the closer the better; • For long lifetime: the larger decay volume the better (CMS/ATLAS is 6-10 m) • For any lifetime: angular coverage the large the better (CMS/ATLAS is 4pi) • LHC main detectors should be competitive in any lifetime (including arbitrary long lifetime limit; some timesBetter people call a lifetime frontier)! sensitivity Log scale in proper lifetime Zhen Liu Hadron Collider Physics (lecture) KEK 2020 84 For the case of long lifetime…

Not decaying in LHC main detectors will decay in other detectors Zhen Liu Hadron Collider Physics (lecture) KEK 2020 85 ≠ Rebuilding intuition: True Potential of main detectors

Log scale in sensitivity in model parameters What we see in or observable rate the LHC (e.g., Br H->XX) projections

True potentials at the LHC main detectors Better sensitivity Log scale in proper lifetime (m) Zhen Liu Hadron Collider Physics (lecture) KEK 2020 86 Reexamining intuition: Identifying the challenge

e.g., C. Csaki, E. Kuflik, S. Lombardo, O. Slone, 1508.01522 shows Higgs to LLPs typical trigger efficiency <1%; ZL, B.Tweedie, 1503.05923, O(100 GeV) LLPs have typical efficiency ~1%;

= × × × 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑 𝒏𝒏𝒔𝒔𝒔𝒔𝒔𝒔 𝑵𝑵𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑 𝑷𝑷𝒊𝒊𝒊𝒊 𝝐𝝐𝒕𝒕O(1%)𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕𝒕∗𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 1-𝝐𝝐100%𝒃𝒃𝒃𝒃𝒃𝒃 20-50% for Energy dedicated threshold, LLP trigger reconstruction efficiency, etc.

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 87 Insight: New useful timing information

= 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 + 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 𝑆𝑆𝑆𝑆 𝐿𝐿𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝐿𝐿𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝐿𝐿𝑏𝑏𝑏𝑏𝑏𝑏 Δ𝑡𝑡 signal − 𝑆𝑆𝑆𝑆 𝛽𝛽𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝛽𝛽𝑐𝑐푐𝑐𝑐𝑐𝑐𝑐𝑐 background𝛽𝛽𝑏𝑏𝑏𝑏𝑏𝑏 arrival time arrival time Slow Delay is a universal feature of Long-Lived Particles*

Liu, ZL, Wang, 1805.05957

Minimal travel time to timing layer is ~4 ns, with 30 ps resolution: 1% delay can be spotted (corresponding to boost factor of 7) LLP (with mass > 10s of GeV) are all delayed! 𝛾𝛾 88 Late comers will be spotted easily

CMS has already conducted a successful search for delayed jet Liu, Liu, Wang, 18’ 8 TeV result by Liu, Tweedie,89 15’ Late comers will be spotted easily

Delayed Jet analysis carried out by CMS

Displaced jet at 13 TeV

More to come: CMS MTD upgrade ATLAS HGTD upgrade Ecal, Muon system, Hcal, timing information to be used Liu, ZL, Wang, 1805.05957 8 TeV results, ZL, Tweedie, 1503.05923 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 90 HGCAL potential

CMS DV new result!

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 91 Part II: Selected Topics Current Status & Bright Future Higgs Precision BSM Broad Brush Rethink about Long-Lived Particles Outlook BSM Opportunities Around the Higgs New effects, e.g., interferences; Beyond minimal/vanilla modes, e.g., as portals Go Exotic Hidden sector dynamics Long-Lived Particles Have Fun Model Agnostic Searches (Anomaly detection) Seeing color flow through interference New metric definition for machines (& pheno) Open data (learn QCD from data?) True Quirk signatures Zhen… Liu Hadron Collider Physics (lecture) KEK 2020 93 Concluding Remarks The success of the LHC (and the SM) has triggered a paradigm shift • chance for us to define new questions/quests, testability is always the backbone; • work (as a community)BSM less like Opportunities a (no over-density for a given topic); what hasn’t changed is we are driven by curiosity, and The BSM Opportunities atAround colliders reside the inHiggs our creative work! Many more: Go Exotic Flavor; QCD; Have Fun EWPO; Machine Learning; … Join Snowmass, help shaping the future of the field https://snowmass21.org/energy/start

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 94 10 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 0 Around Higgs

CMS 1908.01115 ATLAS (re-interpretation), PRL, 17’

Djouadi, Maiani, Polosa, Quevillon, Riquer, 1502.05653 Kling, Su, Su, 2004.04172 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 101

One Key ingredient (recent search)

𝝓𝝓 → 𝒕𝒕𝒕𝒕̅

D. Dicus, A. Stange, S. Willenbrock, hep-ph/9404359, Focusing on ttbar @LHC, M. Carena, ZL, arXiv:1608.07282 Other channels and effects, including ttH, tH (see in N. Craig, F. D’Eramo, P. Drapper, S. Thomas, H. Zhang arXiv:1504.04630 and J. Hajer, Y.-Y. Li, T. Liu J. Shiu arXiv:1504.07617, S. Gori, I.-W. Kim, N. Shah, K. Zurek arXiv:1602.02782 , N. Craig, J. Hajer, Y. Li, T. Liu, H. Zhang, arXiv:1605.08744, B. Hespel, F. Maltoni, E. Vryonidou arXiv:1606.04149, W.S. Hou, M. Kohda, T. Modak 1710.07260, 1906.09703), H+jet, charged Higgs searches, and how stable such effects are against QCD corrections (see a case study in W. Bernreuther, P. Galler, C. Mellein, Z.-G. Si, P. Uwer arXiv:1511.05584), ttbar differential observables ( W. Bernreuther, P. Galler, C. Mellein, Z.-G. Si, P. Uwer arXiv:1702.06063; W. Bernreuther, L. Chen, Z.-G. Zhen Liu Hadron Collider Physics (lecture) Si, 1805.06658 KEK 2020), Machine Learning, 10 Unfamiliar look of heavy Scalars

Signal Background

Triangle loop function

B.W.

Re. Int.

Im. Int.

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 10

Non-factorizable into signal and background calculation, either described by standard EFT; Interferences onsite Gain new information about width and strong & weak phase; Interesting test for Interference.

Dixon, Siu, hep-ph/0302233 Carena, ZL, Riembau, 1801.00794 Campbell, Carena, Harnik, ZL, 1704.08259 Kauer, Lind, Maierhoefer, Song, 1905.03296 Cjeri, Coradeschi, de Florian, Fidanza, 1706.07331 Other channels: Jung, Sung, Yoon, arXiv:1510.03450, Maltoni, Mandal, Zhao, 1812.08703 arXiv:1601.00006, (dijets) Martin, 1606.03026, Bhattipirolu, Martin, Chen, Heinrich, Jahn, Jones, Kerner, Schlenk, Yokoya 1911.09314 2004.06181 see Bhattiprolu’s talk yesterday. Hoche et al, in progress AlsoZhen (real Liu-part interference): Hadron Dixon, Collider Li, 1305.3854 Physics (lecture) KEK 2020 10 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 105 Zhen Liu Hadron Collider Physics (lecture) KEK 2020 10 ILC Results (global fit) After profiling over the other 12 (11) EFT coefficients, we obtain the distribution of the Higgs trilinear coupling; 2 Δ𝜒𝜒

1h observables only

Comparable precision gained through 1h processes Zhen Liu Hadron Collider Physics (lecture) KEK 2020 107 ILC Results (implication)

Single parameter fit using 2H observable only

Global fit with much enlarged parameter space

Clearly, the ILC 500 GeV trilinear extrapolation: • Not limited by Higgs coupling uncertainties; • 1H trilinear observable even improves the sensitivity; • If Higgs properties worsen by a factor of 3, start limiting the trilinear extrapolation; Zhen Liu• improving Hadron 1h Collider will continue Physics (lecture)to improve the KEK trilinear 2020 extrapolation (other 10 precision Higgs machines help!) Results: complementarities Higgs precision enhances LHC trilinear extrapolation;

HL-LHC also enhances LC trilinear determinations.

Zhen Liu Hadron Collider Physics (lecture) KEK 2020 10